170 STRUCTURE OF THE FLOWER. will be seen that all stages of transition occur between leaves and bracts. Many flowers exhibit in a natural condition a gradual transition between sepals and bracts, and the latter, as already noticed, are readily referable to the leaf as the type. Thus, in the Camellia it is almost impossible to say where the bracts end and the sepals begin. In the Marsh-mallow and Strawberry, again, the five sepals in the flowers of the two respectively alternate with five bracts and the difficulty of distinguishing them is so great that some botanists call both sets of organs by the name of sepals. In many flowers in a natural condition, therefore, there is a striking resemblance between FIG. 205.-Abnormal or monstrous Primrose flower, with the sepals converted into true leaves. (From Lindley.) sepals and leaves; and this analogy is at once proved to demonstration by the fact that in monstrous or abnormal flowers of the Rose, Clover, Primrose (Fig. 205), and other plants, the sepals are frequently converted into true leaves. We now pass to the petals, and although these in the majority of flowers are of a different color to leaves and sepals, yet in their flattened character and general structure they are essentially the same; and their analogy to leaves is also proved in many natural flowers by the gradual transitions exhibited between them and the sepals. This is remarkably the case in the White Water-lily, where the flowers present several whorls of floral envelopes, which so resemble one another in their general appearance and color that it is next to impossible to say where the sepals end and the petals begin. In many other instances, also, there is no other way of distinguishing between the parts of the calyx and those of the corolla than by their different positions-the calyx being the outer series, the corolla the STRUCTURE OF THE FLOWER. 171 inner. The analogy between petals and leaves is still further shown by the fact that the former are occasionally green, as in certain species of Cobaa, and also from their being occasionally converted, either entirely or partially, into leaves. We therefore conclude that petals, like sepals and bracts, are homologous with leaves. The stamen is, of all organs, the one which has the least resemblance to the leaf. If its structure, however, be carefully examined, the different parts of the leaf may be clearly recognized in those of the stamen; moreover, we find that in many plants the petals become gradually transformed into stamens. This is remarkably the case in the White Water-lily; thus in the flowers of this plant the inner series of petals gradually become narrower, and the upper extremity of each petal exhibits at first two little swellings, which, in those placed still more internal, become true anthers containing pollen. From the fact that the stamens can thus be shown to be merely modified petals, while the latter have been already proved to be modified leaves, it must necessarily follow that the stamens are so also. If we now refer to what takes place in many cultivated flowers, we have conclusive evidence of the leaflike nature of stamens. Thus, in what are called double flowers, the number of petals is principally increased by the conversion of stamens into petals. Thus, if a double Rose be examined, all sorts of transitions may be observed between true petals and stamens. In other cases the stamens have been actually transformed into true leaves. As far as the stamens, therefore, we have no difficulty in tracing, both in the normal and abnormal conditions of the parts of the flower, a regular and gradual transition from the ordinary leaves. As regards the carpel, we find that transitional states between the stamen and carpel are unknown in the normal condition of flowers, the difference in the functions performed by them respectively being so opposite that it ne 172 STRUCTURE OF THE FLOWER. cessarily leads to corresponding differences in structure. We must, therefore, look to monstrosities or deviations from ordinary structure for examples of such conditions. Even these are by no means common. Such may, however, be occasionally found in the Houseleek, some Poppies, and in other plants. In a paper published by the author in the "Pharmaceutical Journal" for March, 1856, a very remarkable instance of this transition from stamens to carpels was described; it occurred in the Papaver bracteatum. Such examples clearly prove that the stamens and carpels are formed upon a common type, and hence that the latter are, like the former, homologous organs with leaves. The analogy of the carpel to the leaf is, however, constantly shown in cultivated flowers. Thus in many double flowers, as in Roses, the carpels, as well as the stamens, become transformed into petals. It is by no means rare, again, to find the carpels transformed into true leaves, as in the Double Cherry (Figs. 149-151), as already fully described when speaking of the carpel. We have, therefore, as regards the carpel, the most conclusive evidence of its being formed upon a common type with the leaf, and that it is consequently homologous with it. The carpel being thus shown to be homologous with the leaf, it must necessarily follow that the fruit is likewise a modified condition of the leaf, since it is formed of one or more carpels in a matured state. Further proof of the homologous nature of the parts of the flower to the leaf is afforded by the fact that the floral axis, instead of producing flowers, will sometimes bear whorls of true leaves. In other cases the axis becomes prolonged beyond the flower, as in cultivated Roses (Fig. 206), or beyond the fruit (Fig. 207), and becomes a true branch bearing leaves. To this elongation of the axis the term median prolification is usually applied. When a sepal becomes a petal, or a petal a stamen, or a stamen a carpel, the changes which take place are said STRUCTURE OF THE FLOWER. to be owing to ascending or direct metamorphosis. 173 But when a carpel becomes a stamen, or a stamen a petal, or a petal a sepal, or if any of these organs become transformed into a leaf, this is called retrograde or de scending metamor phosis. We have thus proved by the most conclusive facts that all the organs of the flower are formed upon a common type with the leaf, and differ only in their special development; or, in other words, that they are homologous parts. Hence a flower-bud is analogous to a leafbud, as we have already stated (page 169), and FIG. 206. FIG. 207. FIG. 206.-Abnormal or monstrous development in the Rose, showing the axis prolonged beyond the flower and bearing true leaves. FIG. 207.--A monstrous or abnormally developed Pear, showing the axis prolonged beyond the fruit, and bearing true leaves. the flower itself to a branch the internodes of which are but slightly developed, so that all its parts are situated in nearly the same plane; and, as flower-buds are thus analogous to leaf-buds, their parts are also necessarily subject to similar laws of development and arrangement, and hence a knowledge of the latter gives the clew to that of the former. CHAPTER V. REPRODUCTIVE ORGANS OF FLOWERLESS PLANTS. HAVING in former chapters briefly alluded to the nutritive organs of Flowerless plants, we will now describe their Reproductive organs as fully as our space will allow. They are termed Flowerless because they have no true stamens or carpels; but they have analogous organs, more or less concealed or obscure, and hence they have been called Cryptogamous, which means concealed sexes. Having no flowers, they can have no seeds with contained embryo; but they form reproductive bodies called spores, consisting usually of one cell with one or two coats inclosing granular and other matters. Hence, spore-bearing plants are said to be acotyledonous. As here used, the word spore means an asexual reproductive cell. Spores commonly grow by an indefinite extension of one or both their membranes; but there are some exceptions to this, as will appear hereafter. Cryptogamous plants have been arranged in two great divisions, called Cormophytes and Thallophytes. SECTION I. REPRODUCTIVE ORGANS OF CORMOPHYTES. Cormophytes, or Acrogens, have been divided into the Natural Orders Filices, Equisetacea, Marsileacea, Lycopodiacea, Muci, and Hepaticaceæ. 1. Filices or Ferns.-The fructification of these plants consists of little somewhat rounded cases, called |